Glaucoma is a major cause of blindness in the world and is characterized by a loss of retinal ganglion cells. Although the disease is closely associated with elevated intraocular pressure (IOP), it is unclear how this pressure leads to cell death. This proposal is based upon the novel hypothesis that elevated IOP triggers the release of ATP which over-stimulates cytotoxic P2X7 receptors on retinal ganglion cells. Evidence for pressure-dependent ATP release will be confirmed using rat models of glaucoma, while the toxic effects of P2X7 receptor stimulation will be determined in vivo. The pre-apoptotic genes activated by both approaches will be characterized and compared to identify the purinergic component of the response to pressure in vivo. The mechanisms underlying the release of ATP and of P2X7 receptor stimulation will be probed on a cellular level. The role of pannexin hemichannels in the ATP release that accompanies ganglion cell stretch and swelling will be determined, and the ability of this released ATP to autostimulate P2X7 receptors on ganglion cells will be evaluated by recording intracellular calcium levels and whole cell ion currents. Combining in vivo evidence for excess ATP with the identification of the responsible mechanisms ensures this proposal will be both innovative and relevant, providing new insight into how increased pressure damages ganglion cells in glaucoma. PUBLIC HEALTH RELEVANCE: This project is based on the hypothesis that retinal ganglion cells are damaged in glaucoma by pressure-dependent release of excess ATP into the retina which stimulates P2X7 receptors on retinal ganglion cells. This proposal will confirm this relationship and explore how this pathological release occurs with the aim of preventing the initial stages of damage in glaucoma.